The present invention relates generally to a combination wheel brake assembly, and more particularly, to a combination brake and wheel hub assembly having a spring applied, hydraulically released brake assembly and improved means for selectively allowing the wheel hub to be freely rotated despite the application of the spring applied brake and loss of hydraulic pressure in the system.
Hydraulically actuated braking systems in many vehicles and other apparatus require a fail-safe braking system which is spring applied and hydraulically released so that it is actuated and applied whenever there is a loss of hydraulic fluid in the system. If no such fail-safe system were present, a loss of hydraulic pressure would normally result in the failure of the braking system. However, with a spring applied, hydraulically released fail-safe brake, the spring applied brake would automatically be actuated upon a failure or loss of hydraulic pressure or if the hydraulic pressure was insufficient to release the brake.
One problem which is created by utilizing a fail-safe brake system such as that described above is the lack of mobility of the vehicle when the fail-safe system is actuated. Because there is no hydraulic or other pressure available to release the spring applied brake, the vehicle is locked in a braked position unless the braking effect of the spring applied brake can be overcome. In the prior art, this was usually accomplished by manually and mechanically releasing the braking pressure applied by the fail-safe brake spring by separating the braking surfaces.